The invention is based on an electrical machine particularly alternative current generator, also known as alternator, for a motor vehicle.
Electrical machines of the above-mentioned type, in particular claw-pole generators, are generally known. U.S. Pat. No. 5,747,913 has disclosed an electrical machine in the form of a generator with a rotor of the claw-pole design with permanent magnets. The permanent magnets disclosed there are accommodated in intermediary spaces of two adjacent, antipolar, claw-shaped poles. The permanent magnets are contained in such a way that the claw-shaped poles have a profile with projections that is essentially T-shaped in the axial direction. After installation, the permanent magnets are disposed underneath the projections of the T-shaped cross sections of the poles so that a centrifugal stress, which comes from the permanent magnets when the rotor is rotated, acts on the projections of the poles and is absorbed there by these poles.
A disadvantage of the manner disclosed there for containing the permanent magnets is that the distance between two successive antipolar poles is reduced by the projections of the T-shaped cross sections and the leakage flux between two adjacent antipolar projections is therefore increased. The increase of the leakage flux stands in contrast to the use of permanent magnets, which are intended to counteract the leakage flux.
However, with the electrical machine according to the invention, in particular a generator and/or claw-pole generator for motor vehicles, with the characterizing features of the present invention, it is possible to insert permanent magnets into the intermediary space between two adjacent, antipolar, claw-shaped poles without reducing the distance between two antipolar poles. In order to achieve this, permanent magnets are inserted into the intermediary spaces between the alternating poles and are each secured by means of a securing element which in particular cannot be magnetically excited. The securing element itself is secured in grooves on both sides, where one groove is let into the longitudinal side of a magnetic north pole and one groove is let into the longitudinal side of an adjacent magnetic south pole.
Advantageous improvements and updates the characteristics disclosed in the main claim are possible by means of the measures taken in the dependent claims.
Through the use of a relatively thin securing element which can therefore be easily deformed, the surface pressure between the permanent magnet and the securing element is low under rotational stress. In addition, the securing element secures the permanent magnet in both its radial and axial position in the rotor.
One possiblility for axially securing the permanent magnets in relation to the respective securing elements is comprised in that tabs are bent away from a base region of the securing element and limit the axial motion. In this connection, it is possible for the bent tabs to exert a clamping force on axial end faces of the inserted permanent magnet. If elongated bent tabs are angled in end regions so that the permanent magnet is at least partially enclosed, it is possible to clamp the permanent magnet in place in the axial direction by means of the tabs and on the other hand, to clamp the permanent magnet in place between the base region and the end regions.
Another possibility is comprised of using an adhesive to glue the permanent magnet to a base region of the securing element, which is merely essentially flat. This also achieves both an axial and radial fixing of the permanent magnet.
Inserting the base region, together with the permanent magnet, into the grooves is simplified if the base region of the securing element is tapered on at least one axial end. It is easy to fix the axial position of the securing element, together with the permanent magnet, in the rotor because at each axial end of the unit, at least one of the grooves is narrowed in its cross section by means of caulking. Both edges of each claw-shaped pole must be machined in such a way that the grooves assume a precisely determined position.
The machining of the north and south pole edges of the north and south claw poles that extend from each magnet wheel disk is simplified because on end faces of the magnet wheel disk that are oriented axially outward, the stator or rotor has reference elements at uniformly spaced angular intervals. These reference elements permit an alignment of the poles in relation to a tool, for example a groove tool.